The development came as police released the final two of 20 suspects detained in connection with the Ariana Grande concert bombing that killed 22 people and wounded 200 others.

Detectives believe Abedi assembled the deadly nailbomb himself but have not yet established whether he acted alone in obtaining bomb-making materials before he left the country on 15 April.

Jackson said detectives were “relentlessly pursuing” several critical lines of inquiry, including whether others knew that he was storing materials in a white Nissan Micra purchased by Abedi two days before he left for Libya. The car was later found in Rusholme, less than two miles from Abedi’s house in Whalley Range, south Manchester.

A spokesman for Libya’s special deterrence force, which captured Hashem Abedi last month, said on Thursday that the 20-year-old had admitted to helping his older brother prepare for the attack.

In an interview with Reuters news agency, Ahmed bin Salem, the group’s spokesman, said: “Hashem said that he bought all the necessary things for Salman for the attack from the UK and added that Salman was planning to carry out an attack but he did not know where.”

In a statement on the latest developments in the fast-moving investigation, Jackson said on Sunday: “Hashem Abedi is currently detained in Libya. There is much media reporting about what he has said in Libya and we wish to interview him in relation to this attack.

“This was a premeditated, calculated and vicious attack. It was planned carefully and has caused devastation and heartbreak to so many. We have a massive team still working flat-out on it and there are critical lines of inquiry at home and abroad which we will relentlessly pursue.”

Jackson said evidence of explosives had been found at several of the 29 houses searched and each location had links to Abedi.

The Manchester-born bomber seemed “intent on committing the attack within days” of returning to Britain from Libya on 18 May, police said, as Abedi was captured on CCTV buying parts for the bomb, including nuts from a DIY store that were used as shrapnel.

Detectives said the white Nissan Micra contained “considerable evidence” and was used to store items for the explosive device while Abedi was in Libya. Police released new images of the R-registration car and appealed for the public’s help to locate it on 14 April, when detectives believe it was parked with bomb components inside.

Jackson said the 20 people who had been released had been interviewed several times about their association and contact with Abedi. He added: “During the investigation, we have uncovered a number of suspicious purchases of materials by individuals which can be used to make explosives.

“We have identified contact with Abedi that occurred close to the attack time and in some cases the presence of people of interest to the inquiry in Manchester city centre on the evening of the attack. Although this is not the case for every person, it is factors such as these that have led us to make arrests.

“Some of those arrested and now released have offered accounts which explain innocent contact with Abedi and we are, at this time, satisfied with these explanations. However, this has taken a considerable amount of time to work through to ensure we are satisfied and that the risk to the public has been considered. As more information comes in it will be acted upon immediately.”

Jackson said Abedi was identified by detectives as the culprit within two hours of the attack, which he said had triggered one of the biggest investigations in Greater Manchester police’s history.

It has involved more than 1,000 officers, hundreds of witnesses, hundreds of hours of CCTV footage and the seizure of more than 700 electronic devices such as mobile phones and computers.

Jackson said: “This is very much a live criminal investigation moving at considerable speed. It is a terrorism investigation relating to 22 murders and multiple attempted murders. It will continue at its current pace as we work to understand the full extent of the involvement of anyone else.

“We will be speaking with more people. Work around CCTV, financial transactions and telephone contacts will continue as we piece together the movements of Abedi in fine-grain detail.”